This invention relates to a picture display device suitable for displaying an oscilloscopic image on a display screen for displaying a picture formed line and field-sequentially. The picture is composed of pixels and a given number of picture line. The display device provides a location-dependent, determined brightness drive of the pixels during line periods and field or frame periods covering these line periods which results in the oscilloscopic image. The picture display device, therefore includes a signal comparison circuit having a first input for applying a signal which determines the location during a field or frame period, a second input for applying a signal occurring at the line frequency and having a waveform profile to be displayed oscilloscopically during the line periods, and an output supplying a brightness drive signal.
A picture display device of this type is known from European Patent Application No. 0,125,372 which corresponds to U.S. Pat. No. 4,540,938 (9/10/85). The picture display is based on the line and field-sequential structure as is used for television in its broadest sense. Examples are: broadcasting services, monitoring control of areas and spaces, X-ray or infrared picture display, display of computer-generated images, etc., with moving or still pictures in all cases. Combined with these pictures, there is the desired oscilloscopic image as a waveform profile on the screen, which is obtained by the controlled brightness drive of selected pixels. In this case the signal comparison circuit is in the form of an analog differential amplifier which supplies the brightness drive signal as an amplified, cut-off difference signal which ensures the drive after forming an absolute value, a level shift and a signal inversion. To this end the signal determining the location during the field or frame period is applied in the form of a sawtooth signal to the first input of the signal comparison circuit. It is apparent that the known picture display device operates on an analog basis, which inherently implies an inaccurate determination of the location.